Various semiconductor materials are used as electrode elements in photoelectrochemical cells (PECs). The impingement of light radiation on the surface of such cells results in electron-hole pair generation, which can be manifested in a photogenerated current when the semiconductor material is properly connected in an electrical circuit. Converse processes can occur in which an electrical current passed through the material will result in the emission of visible or near visible radiation from the material. The emitted light generally has a spectral density which is characteristic of the material. Some of these materials display photoluminescence, in that light is emitted from the material at its characteristic spectrum upon excitation by external light impinging on its surface.
Interfacial charge-transfer processes at semiconductor electrodes have been actively investigated, and among the most widely studied semiconductor electrodes is n-type cadmium selenide (CdSe). The popularity of CdSe derives in part from its relatively small band gap, in the range of 1.7 eV, and the ease with which single-crystal, polycrystalline, and thin film samples can be fashioned into electrodes for PEC usage. Photoluminescence can be perturbed and electroluminescence initiated in single-crystal, n-type CdSe electrodes by interfacial charge-transfer processes. Investigations of photoluminescence and electroluminescence in CdSe indicate that photoluminescence and electroluminescence occur from a common excited state but under some conditions may originate at different depths from the surface of the semiconductor material.
Such substrates can be employed as the active electrode in a photoelectrochemical cell. It has been found that the application of a voltage between the CdSe electrode and a counterelectrode immersed in the electrolyte of the PEC will result in a quenching of the magnitude of photoluminescence from the active electrode at certain applied voltages. The intensity of light emitted by electroluminescence is also found to vary with the applied voltage where a suitable electrolyte is used to facilitate emission. See: Streckert, H. H.; Tong, J.; Ellis, A. B., Luminescent Photoelectrochemical Cells, J. Am. Chem. Soc., Vol. 104 No. 2, 1982, pp. 581-588. With such electrode material, it is found that only the emission intensity and not its spectral distribution is significantly affected by the potentials utilized.